Áp dụng hệ thức lượng trong tam giác vuông ABC : 

\(AB^2=HB\cdot BC\)

\(\Leftrightarrow AB^2=HB\cdot\left(HB+HC\right)\)

\(\Leftrightarrow3^2=HB^2+3.2HB\)

\(\Leftrightarrow HB^2+3.2HB-9=0\)

\(\Leftrightarrow\left[{}\begin{matrix}HB=1.8\left(N\right)\\HB=-5\left(L\right)\end{matrix}\right.\)

Ta có: \(BH+HC=BC\Rightarrow BC=BH+3,2\)

Áp dụng hệ thức lượng:

\(AB^2=BH.BC\)

\(\Leftrightarrow3^2=BH.\left(BH+3,2\right)\)

\(\Leftrightarrow BH^2+3,2BH-9=0\) (bấm máy phương trình bậc 2: \(x^2+3,2x-9=0\))

\(\Rightarrow\left[{}\begin{matrix}BH=-5< 0\left(loại\right)\\BH=1,8\end{matrix}\right.\)

Vậy \(BH=1,8\left(cm\right)\)

tam giác ABC vuông tại A có đường cao AH

\(\Rightarrow AB^2=BH.BC=BH\left(BH+CH\right)\Rightarrow3^2=BH\left(BH+3,2\right)\)

\(\Rightarrow BH^2+3,2BH=9\Rightarrow BH^2+\dfrac{16}{5}BH-9=0\)

\(\Rightarrow5BH^2+16BH-45=0\Rightarrow\left(BH+5\right)\left(5BH-9\right)=0\)

mà \(BH>0\Rightarrow BH=\dfrac{9}{5}\) (cm)

^{_{Chỗ này là để hỏi những câu mình không biết làm chứ không phải chỗ để dựa dẫm vào nhé :)}} 

He always drives his car out of the garage at nine o'clock in the morning

They rarely find a parking place near the shops

I sometimes fly with my parents to Florida in spring

She often comes late to school in winter

They always meet their friends at the sports ground after dinner

She always enjoys swimming in our pool in the morning

On Mondays my mother always does the washing

I put out the dustbins once a week

We often go for a walk with a dog

My sister sometimes does the ironing

hi viet anh!How the going?I am gread.I am visting Thai Binh with my sister.This phace is where i was born.It is rounden 5 years when i leave here.it has changed a lot of tangle.Well, i often phayed with my friends here,too.

You will want to try the food here.You should come here with us..Why not?

We will wait you in front of the first bakery.ok?

Bye,love you,Otaku.

( hãy cho tôi nghen và chăm học ta hơn đi nhé)

From :anh @gmail.com

To:linh @gmail .com

Subject:My best friend

Hello Linh,

It's great to hear from you . I want to tell you about my best friend.

        My Hang is my best friend .She is 12years old.She lives in VinhPhuc with her parents . She is a studen in Dong Tinh secondary school .

        She s English because it helps her broaden her know ledige .She often helps me study English .She is very friendly and kind .I love my best friend 

      what about you ? who's your my best friend ?

 From : hime@gmail.com

To     : nguyenvy@gmail.com

Subject : My best friend

Hello Vy ,

How are you ? It's great to hear from you. Now, I want to tell you about my best friend.

Linh is my best friend. She is 12 years old. She is in grade 6. She lives in Binh Giang with our family. She s getting up early and watering the flowers in our garden. Her favourite sport is swimming. She spends two hours each day swimming. She has an oval face with long black hair. She has black eyes, a straight nose and full lips. My best friend is kind, friendly and hard-working. She often helps me do my homework. She always listen to me when I'm sad. I love my best friend very much. 

What about you ? Who's your best friend ?

Please write to me soon.

Bye Bye

 Huyen.

Bài em cần đâu em?

 (650 - 298 + 350) : (50 : 10 x 2 + 8)

= (650 + 350 - 298) : (5 x 2 + 8)
= (1000 - 298) : (10 + 8)

= 702 : 18

= 39

(650-289+350):(50:10x2+8)

=[(650+350)-289]:(5x2+8)

=(1000-298):(10+8)

=702:18=39

Chúc bạn làm tốt nka <3

39 nha bạn

1b

2c

3c

4c

5a

6b

7d

8b

a: Xét ΔABE và ΔACD có

AB=AC

\(\widehat{A}\) chung

AE=AD

Do đó: ΔABE=ΔACD

\(a,\left\{{}\begin{matrix}AB=AC\\AD=AE\\\widehat{BAC}\text{ chung}\end{matrix}\right.\Rightarrow\Delta ABE=\Delta ACD\left(c.g.c\right)\\ b,\Delta ABE=\Delta ACD\\ \Rightarrow\widehat{AEB}=\widehat{ADC}\\ \Rightarrow180^0-\widehat{AEB}=180^0-\widehat{ADC}\\ \Rightarrow\widehat{BDC}=\widehat{CEB}\)

4 xe a, b, c, d chở được là:

3 + 4,5 = 7,5 (tấn)

Xe e chở được là:

(7,5 : 4) + 1 = 2,9

Bài 3 nhé!

Em cần bài nào em?